250ml white balsamic vinegar
500g red onions, sliced
1 In a large bowl, stir the sugar into the white balsamic vinegar. The sugar does not need to be completely dissolved.
2 Add the onions and leave them to steep for at least 24 hours. They can be kept chilled, in the pickling liquid, for up to one week.
Tip: Chef uses Tropea onions from Italy, which are sweeter, thicker and fleshier than regular onions. Grab hold of a bag if you spot them in the supermarkets; they are equally good raw or pickled.